Exhaust Treatment System With Hydrocarbon Lean NOx Catalyst

ABSTRACT

A system for treating an exhaust stream from an engine includes a main exhaust passageway adapted to receive the exhaust stream from the engine. A side branch is in communication with the main exhaust passageway. A regeneration unit is positioned within the side branch for combusting a fuel and heating the exhaust flowing through the main exhaust passageway. A lean NO x  catalyst is positioned within the main exhaust passageway downstream of the regeneration unit. A reductant injector is positioned downstream of the regeneration unit and upstream of the lean NO x  catalyst to inject reductant particles into the exhaust stream. A controller operates the regeneration unit to increase the exhaust temperature as well as operates the reductant injector to reduce NO x  within the lean NO x  catalyst.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application Ser. No. 12/430,194, filed on Apr. 27, 2009. This application claims the benefit of U.S. Provisional Application No. 61/433,297 filed on Jan. 17, 2011. The entire disclosures of the above applications are incorporated herein by reference.

FIELD

The present disclosure generally relates to a system for treating exhaust gases. More particularly, a device for increasing an exhaust gas temperature upstream of a hydrocarbon lean NO_(x) catalyst is discussed.

BACKGROUND

In an attempt to reduce the quantity of NO_(X) and particulate matter emitted to the atmosphere during internal combustion engine operation, a number of exhaust aftertreatment devices have been developed. A need for exhaust aftertreatment systems particularly arises when diesel combustion processes are implemented. Typical aftertreatment systems for diesel engine exhaust may include one or more of a diesel particulate filter (DPF), a selective catalytic reduction (SCR) system, a hydrocarbon (HC) injector, and a diesel oxidation catalyst (DOC).

During engine operation, the DPF traps soot emitted by the engine and reduces the emission of particulate matter (PM). Over time, the DPF becomes loaded and begins to clog. Periodic regeneration or oxidation of the trapped soot in the DPF is required for proper operation. To regenerate the DPF, relatively high exhaust temperatures in combination with an ample amount of oxygen in the exhaust stream are needed to oxidize the soot trapped in the filter.

The DOC is typically used to generate heat to regenerate the soot loaded DPF. When hydrocarbons (HC) are sprayed over the DOC at or above a specific light-off temperature, the HC will oxidize. This reaction is highly exothermic and the exhaust gases are heated during light-off. The heated exhaust gases are used to regenerate the DPF.

Under many engine operating conditions, however, the exhaust gas is not hot enough to achieve a DOC light-off temperature of approximately 300° C. As such, DPF regeneration does not passively occur. Furthermore, NO_(X) adsorbers and selective catalytic reduction systems typically require a minimum exhaust temperature to properly operate.

A burner may be provided to heat the exhaust stream upstream of the various aftertreatment devices. Known burners have successfully increased the exhaust temperature of internal combustion engines for automotive use. Some Original Equipment Manufacturers have resisted implementation of prior burners due to their size and cost. Furthermore, other applications including diesel locomotives, stationary power plants, marine vessels and others may be equipped with relatively large diesel compression engines. The exhaust mass flow rate from the larger engines may be more than ten times the maximum flow rate typically provided to the burner. While it may be possible to increase the size of the burner to account for the increased exhaust mass flow rate, the cost, weight and packaging concerns associated with this solution may be unacceptable. Therefore, a need may exist in the art for an exhaust treatment system equipped with a hydrocarbon lean NO_(x) catalyst and a device to increase the temperature of the exhaust output from an engine while minimally affecting the cost, weight, size and performance of the exhaust system. It may also be desirable to minimally affect the pressure drop and/or back pressure associated with the use of a burner.

SUMMARY

This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.

A system for treating an exhaust stream from an engine includes a main exhaust passageway adapted to receive the exhaust stream from the engine. A side branch is in communication with the main exhaust passageway. A regeneration unit is positioned within the side branch for combusting a fuel and heating the exhaust flowing through the main exhaust passageway. A lean NO_(x) catalyst is positioned within the main exhaust passageway downstream of the regeneration unit. A reductant injector is positioned downstream of the regeneration unit and upstream of the lean NO_(x) catalyst to inject reductant particles into the exhaust stream. A controller operates the regeneration unit to increase the exhaust temperature as well as operates the reductant injector to reduce NO_(x) within the lean NO_(x) catalyst.

A system for treating an exhaust stream from an engine includes a burner for combusting a fuel and heating the exhaust flowing through an exhaust passageway. A lean NO_(x) catalyst is positioned within the exhaust passageway downstream of the burner. A reductant injector is positioned upstream of the burner and upstream of the lean NO_(x) catalyst to inject reductant particles into the exhaust stream. A controller operates the burner to increase the exhaust temperature as well as operates the injector to reduce NO_(x) within the lean NO_(x) catalyst.

A system for treating an exhaust stream from an engine includes a burner for combusting a fuel and heating the exhaust flowing through an exhaust passageway. A lean NO_(x) catalyst is positioned within the exhaust passageway in direct receipt of the exhaust heated by the burner prior to passing through another catalyst. A hydrocarbon injector is positioned downstream of the burner and upstream of the lean NO_(x) catalyst to inject hydrocarbon into the exhaust stream. A controller operates the burner to increase the exhaust temperature to a predetermined magnitude for burning carbon deposits positioned at active sites within the lean NO_(x) catalyst.

Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.

FIG. 1 is a schematic depicting a system for controlling the temperature of an exhaust from an engine;

FIG. 2 is a sectional side view of a portion of the exhaust aftertreatment system depicted in FIG. 1 including a miniature regeneration unit;

FIG. 3 is a cross-sectional view of an alternate regeneration unit;

FIG. 4 is a cross-sectional view of an alternate regeneration unit;

FIG. 5 is a cross-sectional view of an engine aftertreatment system including a flow diverter;

FIG. 6 is a perspective view of the aftertreatment system including the flow diverter;

FIG. 7 is a partial perspective view of a portion of another alternate regeneration unit;

FIG. 8 is a cross-sectional view of another alternate regeneration unit;

FIGS. 9-13 are perspective views depicting alternate inlet tube portions of the regeneration unit;

FIG. 14 is a sectional view depicting another alternate exhaust aftertreatment system;

FIGS. 15-19 depict alternate exhaust aftertreatment systems including a regeneration unit and a hydrocarbon lean NO_(x) catalyst; and

FIGS. 20 and 21 depict alternate exhaust gas aftertreatment systems including a burner and a hydrocarbon lean NO_(x) catalyst.

Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.

DETAILED DESCRIPTION

Example embodiments will now be described more fully with reference to the accompanying drawings.

FIG. 1 depicts an exhaust gas aftertreatment system 10 for treating the exhaust output by an exemplary engine 12 to a main exhaust passageway 14. An intake passage 16 is coupled to engine 12 to provide combustion air thereto. A turbocharger 18 includes a driven member (not shown) positioned in an exhaust stream. During engine operation, the exhaust stream causes the driven member to rotate and provide compressed air to intake passage 16 prior to entry into engine 12.

Exhaust aftertreatment system 10 also includes a miniature regeneration unit 26 positioned downstream from turbocharger 18 and upstream from a number of exhaust aftertreatment devices. In the exemplary aftertreatment system depicted in FIG. 1, the aftertreatment devices include a hydrocarbon injector 28, a diesel oxidation catalyst 30 and a diesel particulate filter 32.

Regeneration unit 26 is positioned within a side branch portion 34 of system 10 in communication with main exhaust passageway 14. Regeneration unit 26 may be used to heat the exhaust passing through passageway 14 to an elevated temperature that will enhance the efficiency of DOC 30 and allow regeneration of DPF 32.

Regeneration unit 26 may include one or more injectors 36 for injecting a suitable fuel and an oxygenator. The fuel may include hydrogen or a hydrocarbon. Injector 36 may be structured as a combined injector that injects both the fuel and oxygenator, as shown in FIG. 1, or may include separate injectors for the fuel and the oxygenator (FIG. 11). A control module 38 is provided to monitor and control the flows through the injector 36 and the ignition of fuel by a first igniter 42 using any suitable processor(s), sensors, flow control valves, electric coils, etc.

Regeneration unit 26 includes a housing 50 constructed as a multi-piece assembly of fabricated metal components. Housing 50 includes an inlet tube 52, a cylindrically-shaped body 54, and an outlet tube 56. An inlet header 58 is fixed to inlet tube 52. Inlet header 58 is fixed to side branch portion 34 and encloses one of its ends. Other single or multi-piece inlet assemblies are also contemplated as being within the scope of the present disclosure. An annular volume 62 exists in a space between an inner surface 64 of side branch portion 34 and an outer surface of housing 50.

An injector mount 65 is fixed to inlet tube 52 and/or inlet header 58 to provide an attachment mechanism for injector 36. A nozzle portion 66 of injector 36 extends into inlet tube 52 such that atomized fuel may be injected within a primary combustion chamber 68 at least partially defined by an inner cylindrical surface 70 of body 54. Injector 36 includes a fuel inlet 72 and an air inlet 74. Fuel inlet 72 is in communication with a fuel delivery system 76 including a fuel tank 78, a fuel filter 80, a fuel pump 82 and a fuel block 84 interconnected by a fuel line 86. Operation of the components of fuel delivery system 76 selectively provides hydrocarbon to injector 36.

A secondary air system 90 includes a secondary air filter 92 and a MAF sensor 94. A compressor 96 is in receipt of air that is passed through secondary air filter 92 and MAF sensor 94. Compressor 96 may include a portion of a supercharger, a turbocharger or a stand-alone electric compressor. Output from compressor 96 is provided to air inlet 74. When exhaust heating is desired, fuel is injected via fuel inlet 72 and the oxygenator is provided via air inlet 74 to inject a stream of atomized fuel. First igniter 42 is mounted to side branch portion 34 downstream of inlet header 58 and is operable to combust the fuel provided by injector 36 within primary combustion chamber 68.

Side branch portion 34 intersects exhaust passageway 14 at an angle A of substantially 30 degrees. The flame produced by regeneration unit 26 extends into exhaust passageway 14 at substantially the same angle.

An elongated aperture 110 extends through a pipe 112 defining main exhaust passageway 14. A portion of body 54 and outlet tube 56 are positioned within exhaust passageway 14. Exhaust provided from engine 12 impinges on housing 50 and cools it during operation of regeneration unit 26. Furthermore, because housing 50 minimally intrudes within passageway 14, exhaust back pressure is also minimally increased. It should also be appreciated that side branch portion 34 and injector 36 minimally radially outwardly extend from pipe 112. Such an arrangement allows an Original Equipment Manufacturer to more easily package the miniature regeneration unit on the vehicle.

In the present aftertreatment system, first igniter 42 also includes an ion sensor 44 coupled to a coil 46. Ion sensor 44 may be in the form of an electrode positioned within combustion chamber 68. A voltage may be applied to the ion sensor to create an electric field from the sensor to a ground such as housing 50. When voltage is applied, an electric field radiates from the sensor to the ground. If free ions are present in the field, a small ion current may flow. The magnitude of the ion current provides an indication of the density of the ions. Control module 38 detects and receives signals from ion sensor 44 to determine the presence or absence of a flame. Ion sensor 44 may also determine if igniter 42 is fouled.

Fouling may occur through deposition of soot, oil or other contaminants. When igniter 42 is fouled, proper combustion may not occur. Control module 38 is operable to supply and discontinue the supply of fuel to fuel inlet 72, air to air inlet 74 and electrical energy to igniter 42. Prior to initiating the supply of fuel and air to injector 36, control module 38 determines whether igniter 42 has been fouled via the signal provided by ion sensor 44. If the igniter is determined to be ready for operation, control module 38 may account for a number of engine and vehicle operating conditions such as engine speed, ambient temperature, vehicle speed, engine coolant temperature, oxygen content, mass air flow, pressure differential across diesel particulate filter 32, and any number of other vehicle parameters. If control module 38 determines that an increase in exhaust gas temperature is desired, fuel and secondary air are provided to injector 36. Coil 46 supplies electrical energy to igniter 42 to initiate combustion within primary combustion chamber 68.

Control module 38 may also evaluate a number of other parameters including presence of combustion and temperature of the exhaust gas within passageway 14 at a location downstream from regeneration unit 26 to determine when to cease the supply of fuel and air to injector 36. For example, control module 38 may receive signals from one or more temperature sensors located within regeneration unit 26, side branch portion 34 or within main passageway 14 to perform a closed loop control by operating regeneration unit 26 to maintain a desired temperature at a particular location. If combustion unexpectedly extinguishes, control module 38 ceases the supply of fuel. Other control schemes are also within the scope of the present disclosure.

FIG. 3 depicts an alternate regeneration unit 26 a coupled to side branch portion 34. Regeneration unit 26 a is substantially similar to regeneration unit 26 except that the reduced or necked-down outlet tube portion of housing 50 has been removed. As such, like elements will be identified with an “a” suffix. Main body portion 54 a includes a substantially constant diameter that terminates at an outlet opening 53 a.

FIG. 4 depicts another alternate regeneration unit identified at reference numeral 26 b. Regeneration unit 26 b is substantially similar to regeneration unit 26 except that a length L has been increased to cause a greater portion of housing 50 b to be positioned within exhaust passageway 14. Like elements will include a “b” suffix. The location of igniter 42 b has been changed to be further from an end of nozzle 66.

FIGS. 5 and 6 depict another alternate arrangement including a diverter plate 140 positioned within pipe 112 upstream of miniature regeneration unit 26. Diverter plate 140 includes a D-shaped aperture 142 extending therethrough. Diverter plate 140 is positioned at an angle as depicted in FIG. 5 to urge exhaust flowing through passageway 14 to flow toward and around housing 50. The diverted exhaust flow transfers heat from regeneration unit 26 to the exhaust flowing through pipe 112.

FIG. 7 depicts a portion of another alternate regeneration unit identified at reference numeral 26 c. Regeneration unit 26 c is substantially similar to regeneration unit 26 except that outlet tube 56 c is increased in length and includes a plurality of apertures 144 extending therethrough. The extended outlet tube length and apertures 144 assure that the combustion flame is properly maintained and directed during operation of regeneration unit 26 c. As exhaust flows through passageway 14, some of the exhaust passes through apertures 144 creating a mixing effect resulting in a more desirable temperature distribution, flame stability and flame quality.

FIG. 8 depicts another alternate regeneration unit identified at reference numeral 26 d. Regeneration unit 26 d includes the components of regeneration unit 26 as well as an additional housing portion 145 defining a secondary combustion chamber 146. A second igniter 148 extends into secondary combustion chamber 146. A plurality of apertures 149 extends through second housing 145 to allow exhaust gas to enter secondary combustion chamber 146. Enhanced exhaust heating and mixing may be achieved through the use of regeneration unit 26 d.

FIGS. 9-13 depict alternate inlet tube configurations that may be used in lieu of inlet tube 52. Each of the modified inlet tubes includes a plurality of circumferentially spaced apart apertures 150 extending through an end wall 152. Apertures 150 allow exhaust gas flowing through passageway 14 to enter primary combustion chamber 68. By providing oxygen into primary combustion chamber 68 via apertures 150, the pressure of secondary air provided by compressor 96 to injector 36 may be reduced. The cost and size of compressor 96 may also be reduced.

Inlet tube 52 e shown in FIG. 9 includes a plurality of flaps 156 e attached at one end to end wall 152 e. Flaps 156 e are arranged to induce gas passing through apertures 150 e to swirl. FIG. 10 depicts rectangularly shaped apertures 150 f with no flaps. FIG. 11 depicts a plurality of flaps 156 g attached at a radial inner extent of apertures 150 g. Flaps 156 g extend at an angle to exhaust flow in a radially outward direction. FIG. 12 refers to another alternate inlet tube assembly 52 h having a plurality of apertures 150 h and a plurality of flaps 156 h. Flaps 156 h radially inwardly extend.

FIG. 13 shows a plurality of circular apertures 150 i circumferentially spaced apart from one another. No flaps partially block the apertures. Each of the arrangements depicted in FIGS. 9-13 provide a substantially homogenous distribution of flow within primary combustion chamber 68.

It is also contemplated that any one of the described miniature regeneration unit arrangements including apertures 150 may be equipped with an injector 36 j having a relocated secondary air inlet 74 j, to inject compressed air at a relatively low pressure into annular volume 62, as shown in FIG. 14. Fuel inlet 72 j positioned to inject atomized fuel within primary combustion chamber 68 j, as previously discussed. Some of the air injected into annular volume 62 j passes through apertures 150 i and the remaining portion of the secondary air passes over an outside surface of housing 50 j to cool miniature regeneration unit 26 j.

FIG. 15 depicts a portion of another exhaust gas aftertreatment system identified at reference numeral 200. System 200 is similar to system 10 depicted in FIG. 1. Accordingly, like elements will retain their previously introduced reference numerals. Exhaust gas aftertreatment system 200 includes a reductant injector 202 positioned immediately downstream from DPF 32. The reductant injector may be configured as an aerosol generator 202. Reductant injector 202 is supplied with a hydrocarbon such as diesel fuel stored within fuel tank 78. In the example shown in FIG. 15, a fuel line 204 supplies fuel from tank 78 to the reductant injector. Other internal combustion engine fuels such as ethanol based fuels including E85, E93, or E95 may be the reductant of choice and stored in a separate on-board container.

Aerosol generator 202 includes an electrically powered heating element. Reductant supplied via fuel line 204 is heated by the heating element. It should be appreciated that the reductant may or may not come into direct contact with a surface of the heating element. Regardless of the arrangement, energy is transferred from the heating element to the reductant to increase the temperature and energy content of the reductant. The heated reductant is injected into the exhaust stream downstream from DPF 32. Based on the nozzle design, reductant pressure and reductant temperature, very small reductant droplets having a size less the one micron are injected into exhaust passageway 14.

A lean NO_(X) catalyst (LNC) 208 and a selective catalytic reduction device (SCR) 210 are mounted within a common housing 214. LNC 208 is positioned upstream of SCR 210 to reduce NO_(X) in an oxygen rich environment. LNC 208 is a hydrocarbon lean NO_(X) catalyst configured to reduce NO_(X) using a hydrocarbon as the reductant. Aerosol generator 202 provides a number of design advantages for exhaust aftertreatment system 200. The heated aerosol mist of reductant exiting aerosol generator 202 is rapidly dispersed throughout the exhaust exiting DPF 32. A minimized length of exhaust conduit is required to provide a mixing zone for the exhaust and reductant prior to entry into LNC 208. The small reductant droplets interact with the porous surface of LNC 208 more efficiently than larger droplets of reductant. Use of aerosol generator 202 results in improved catalyst response from LNC 208. The reduced size droplets also minimize the likelihood of damage to LNC 208 through liquid impingement on the catalyst.

SCR 210 is positioned downstream from LNC 208 to further reduce NO_(X) and remove ammonia from the exhaust stream. As depicted in FIG. 15, LNC 208 and SCR 210 may be positioned adjacent to one another within common housing 214.

Reductant injector 202 may alternatively be configured as a nozzle for supplying unheated and pressurized reductant. Injector 202 may supply an alcohol based internal combustion engine fuel. Based on the volatility of these fuels, an aerosol generator or vaporizer may not be needed to rapidly disperse the reductant in the exhaust.

FIG. 16 depicts a portion of another alternate exhaust gas aftertreatment system identified at reference numeral 300. System 300 is substantially similar to system 200. Accordingly, like elements will be identified by their previously introduced reference numerals. In the arrangement depicted in FIG. 16, the diesel particulate filter has been moved downstream and combined with the SCR. As such, a DPF having an SCR coating is depicted at reference numeral 302. By moving the DPF further downstream, LNC 208 is positioned closer to engine 12 and miniature regeneration unit 26. Accordingly, the temperature of exhaust entering LNC 208 should be greater than a like configuration where LNC 208 is positioned further from the energy sources.

Exhaust gas aftertreatment system 10 takes advantage of the relative position of miniature regeneration unit 26, diesel oxidation catalyst 30 and aerosol generator 202 to maximize the conversion efficiency of LNC 208. The NO_(X) reduction efficiency achieved by LNC 208 increases with the increase of exhaust temperature. Furthermore, it should be appreciated that SCR coated DPF 302 is positioned within sufficient proximity of miniature regeneration unit 26 and diesel oxidation catalyst 30 to selectively regenerate SCR/DPF 302 as required. By using aerosol generator 202 to introduce the reductant, improved distribution and mixing of the reductant with the exhaust gas occurs prior to entering LNC 208. Efficient NO_(X) reduction occurs. Aerosol generator 202 further improves the operating characteristics of LNC 208 by injecting heated reductant. An undesirable reduction in the exhaust temperature is avoided.

FIG. 17 depicts a portion of another alternate exhaust gas aftertreatment system 400. Aftertreatment system 400 relocates LNC 208 further upstream closer to engine 12 and miniature regeneration unit 26. This configuration increases NO_(X) conversion efficiency over a greater range of engine operating conditions including cold starts. Miniature regeneration unit 26 adds heat to the exhaust while aerosol generator 202 adds energy to the reductant injected upstream of LNC 208. Regeneration unit 26 may be positioned upstream of lean NO_(x) catalyst 208 such that carbon deposits may be periodically or continuously burned from the catalyst's active sites. Regeneration of lean NO_(x) catalyst 208 increases the NO conversion efficiency of aftertreatment system 400. It is contemplated that LNC 208 includes a silver-based catalyst for use with alcohol-based reductants such as ethanol, E85, E93, E95 and the like. Acetaldehyde is produced as the active compound in NO reduction at temperatures greater than or equal to 300° C. Through the use of aerosol generator 202, also known as a vaporizer, the alcohol-based reductants may be broken down prior to contact with the silver-based catalyst to cause NO conversion to occur at temperatures lower than 300° C. The use of aerosol generator 202 also increases the overall conversion efficiency at higher catalyst temperatures.

If desired, an optional SCR (not shown) may be positioned immediately downstream from LNC 208 to conduct additional NO_(X) conversion and ammonia reduction. System 400 includes hydrocarbon injector 28 being positioned downstream from LNC 208 and upstream from DOC 30 and DPF 32. DOC 30 and DPF 32 are shown positioned in a common housing 402. To regenerate DPF 32, controller 38 selectively causes hydrocarbon injector 28 to inject a reductant such as diesel fuel into the exhaust stream downstream of LNC 208 and upstream from DOC 30.

FIG. 18 depicts another alternate exhaust gas aftertreatment system 500. Aftertreatment system 500 is substantially similar to aftertreatment system 300. Accordingly, like elements will retain their previously introduced reference numerals. More particularly, system 500 differs from system 300 in that system 500 includes a diesel particulate filter having a lean NO_(X) catalyst coating instead of an SCR coated DPF. Packaging space and cost may be reduced by implementing the solutions shown in aftertreatment system 300 and aftertreatment system 500.

During operation of LNC DPF 502, an exothermic chemical reaction takes place. The release of energy aids in regeneration of soot captured by the diesel particulate filter. Furthermore, regeneration of the DPF may occur simultaneously with desulfation of the hydrocarbon LNC. SCR 210 is positioned downstream from LNC/DPF 502 to remove ammonia and further reduce NO_(X).

FIG. 19 shows another alternate exhaust gas aftertreatment system 600. Exhaust gas aftertreatment system 600 is substantially similar to aftertreatment system 500. These systems are substantially the same other than aerosol generator 202 is replaced with a second reductant injector 602. Second reductant injector 602 is plumbed in communication with a supplemental storage tank 604. A second reductant such as an alcohol based fuel is stored within tank 604 and selectively supplied to second reductant injector 602. Alcohol based fuels such as E85, E93 and E95 provide an enhanced NO_(X) reduction efficiency when compared to the use of diesel fuel as a reductant. An injector may be used to inject the alcohol based fuel instead of an aerosol generator due to the low vapor pressure of the second reductant. Filling tank 604 with a readily available alcohol based fuel is considered to be desirable when compared to storing and dispensing a source of ammonia such as urea.

FIG. 20 depicts another exhaust gas aftertreatment system 700 equipped with LNC 208 and SCR/DPF 302 packaged in a common housing 702. Aerosol generator 202 is positioned in communication with exhaust passageway 14 upstream of a burner 704. Burner 704 is configured such that all of the exhaust travelling through passageway 14 passes through burner 704 to an inlet 706 of housing 702. System 700 operates such that the atomized reductant provided by aerosol generator 202 is heated by burner 704 but not combusted by the flame produced within burner 704. As such, a reductant laden and heated exhaust is provided to inlet 706 to achieve an improved operating range and better cold start performance of LNC 208. Burner 704 is configured with a shell 708 to achieve this function. The burner generates a combustion flame within shell 708. The reductant and exhaust mixture passes over an outer surface of shell 708 to allow heat transfer to the exhaust without combusting the reductant.

FIG. 21 depicts another exhaust gas aftertreatment system identified at reference numeral 800. System 800 is substantially similar to system 700 with the exception that aerosol generator 202 is replaced with a secondary reductant injector 802. Secondary reductant injector 802 is supplied with a secondary reductant such as an alcohol based fuel stored in a supplemental reductant tank 804. Injected secondary reductant mixes with exhaust travelling through exhaust passageway 14 and is heated by burner 704. The heated reductant and exhaust is supplied to LNC 208 and SCR/DPF 302 to reduce undesirable NO_(X) emissions.

The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. Additional alternate exhaust gas aftertreatment systems are also contemplated as being within the scope of the present disclosure. For example, previous configurations described as having an aerosol generator may also be configured to include a more typical reductant injector for supplying reductant into the exhaust at its ambient temperature. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure. 

1. A system for treating an exhaust stream from an engine, the system comprising: a main exhaust passageway adapted to receive the exhaust stream from the engine; a side branch in communication with the main exhaust passageway; a regeneration unit positioned within the side branch for combusting a fuel and heating the exhaust flowing through the main exhaust passageway; a lean NO_(x) catalyst positioned within the main exhaust passageway downstream of the regeneration unit; a reductant injector positioned downstream of the regeneration unit and upstream of the lean NO_(x) catalyst to inject reductant particles into the exhaust stream; and a controller to operate the regeneration unit to increase the exhaust temperature as well as operate the reductant injector to reduce NO_(x) within the lean NO_(x) catalyst.
 2. The system of claim 1, further including an oxidation catalyst and a particulate filter positioned within the main exhaust passageway downstream of the regeneration unit and upstream of the reductant injector.
 3. The system of claim 2, further including a selective catalytic reduction device positioned downstream of the lean NO_(x) catalyst.
 4. The system of claim 3, wherein the oxidation catalyst and the particulate filter are positioned in a first housing, the lean NO_(x) catalyst and the selective catalytic reduction device being positioned in a second housing spaced apart from the first housing.
 5. The system of claim 1, wherein the lean NO_(x) catalyst includes a catalyst coated particulate filter.
 6. The system of claim 5, wherein the reductant injector is positioned downstream of the oxidation catalyst and further including a selective catalytic reduction device positioned downstream of the lean NO_(x) catalyst.
 7. The system of claim 1, wherein the reductant injector includes an aerosol generator for heating and injecting reductant.
 8. The system of claim 7, wherein the aerosol generator supplies reductant particles having a size less than one micron in diameter.
 9. The system of claim 1, further including an oxidation catalyst and a particulate filter positioned within the main exhaust passageway downstream of the lean NO_(x) catalyst.
 10. The system of claim 1, further including a hydrocarbon injector positioned downstream of the regeneration unit and upstream from an oxidation catalyst to inject a hydrocarbon into the exhaust stream.
 11. The system of claim 1, further including a particulate filter having a selective catalytic reduction material coating, the coated filter being positioned downstream of the lean NO_(x) catalyst.
 12. The system of claim 1, wherein the reductant injector injects an internal combustion engine fuel.
 13. The system of claim 12, wherein the regeneration unit is positioned immediately upstream of the lean NO_(x) catalyst to provide exhaust at a temperature high enough to burn carbon deposits from active sites within the lean NO_(x) catalyst.
 14. A system for treating an exhaust stream from an engine, the system comprising: an exhaust passageway adapted to receive the exhaust stream from the engine; a burner for combusting a fuel and heating the exhaust flowing through the exhaust passageway; a lean NO_(x) catalyst positioned within the exhaust passageway downstream of the burner; a reductant injector positioned upstream of the burner and upstream of the lean NO_(x) catalyst to inject reductant particles into the exhaust stream; and a controller to operate the burner to increase the exhaust temperature as well as operate the injector to reduce NO_(x) within the lean NO_(x) catalyst.
 15. The system of claim 14, further including a particulate filter having a selective catalytic reduction material coating, the coated filter being positioned downstream of the lean NO_(x) catalyst.
 16. The system of claim 14, wherein the reductant injector includes an aerosol generator for heating and injecting a hydrocarbon reductant.
 17. The system of claim 16, wherein the aerosol generator supplies reductant particles having a size less than one micron in diameter.
 18. The system of claim 14, wherein the reductant includes an alcohol based fuel.
 19. The system of claim 14, wherein the burner includes a shell around which an exhaust and reductant mixture flows, the burner generating a flame positioned within the shell.
 20. A system for treating an exhaust stream from an engine, the system comprising: an exhaust passageway adapted to receive the exhaust stream from the engine; a burner for combusting a fuel and heating the exhaust flowing through the exhaust passageway; a lean NO_(x) catalyst positioned within the exhaust passageway in direct receipt of the exhaust heated by the burner prior to passing through another catalyst; a hydrocarbon injector positioned downstream of the burner and upstream of the lean NO_(x) catalyst to inject hydrocarbon into the exhaust stream; and a controller to operate the burner to increase the exhaust temperature to a predetermined magnitude for burning carbon deposits positioned at active sites within the lean NO_(x) catalyst.
 21. The system of claim 20, wherein the hydrocarbon includes an alcohol based fuel.
 22. The system of claim 20, wherein the hydrocarbon includes diesel fuel.
 23. The system of claim 20, further including an oxidation catalyst and a particulate filter positioned within the main exhaust passageway downstream of the regeneration unit.
 24. The system of claim 20, wherein the reductant injector includes an aerosol generator for heating and injecting the hydrocarbon.
 25. The system of claim 24, wherein the aerosol generator supplies reductant particles having a size less than one micron in diameter. 